Firstly, the only way to make single parenthood less common in African Americans, is to make contraception methods and abortion options more available to the people of this ethnicity. Although both options are available to anyone in the US (I am Canadian, so please correct me if I am wrong), the African American community has the highest poverty rate. Basically, without much money people in this ethnicity are less likely to use protection while having sexual intercourse, as they cost money, which, in turn, can lead to pregnancy. And abortions are expensive, so if someone is certain that they are pregnant and they decide that they want to have an abortion, they would have to resort to a method that could either harm their self or disrupt the fetus without terminating it, which would lead to future medical bills that they are unable to pay for.
Single parenthood is often caused by one parent leaving the full responsibility of their child to the other parent. There are many reasons for this. The first is caused by an individual who, simply, does not want a child, this particular situation is inevitable, as anyone, regardless of ethnicity, could do this. Another cause, however, is more likely to occur to someone who is both poor and a part of the African American community. Most of the time, taking care of children is difficult. A lot of time and money is invested in one's own child. To an individual who is hoping to get accepted into university on a scholarship or trying to get a degree, a child can be very inconvenient. Supporting a child, which likely would involve a job with long hours, could harm the success of someone trying to achieve either of these goals (and many more), and by failing to succeed, it only furthers the cycle of poverty in their community. Scholarships and success in general are harder to come by due to racism so adding the care of a child to the mix does not make it any easier. Of course there are many other reasons why someone might be a single parent. It is not always because someone is simply a douchebag and there just so happens to be more douchebags in the African American community. Sometimes the decisions are hard and painful for the parting parent to make.
As for crime rates, these, again, are usually linked to poverty. Poverty while caring for a child, can lead to stress, which, in turn, could lead to unhealthy coping mechanisms, such as the abuse of drugs and alcohol, which can either be illegal or lead to irrational behaviors. Another thing this could lead to, is the need for "fast money". This could lead an individual to some other crimes, such as, the selling of illegal drugs, theft, robery, etc.